As is known, flight control of a modern turbine engine aircraft calls for constant monitoring of a number of parameters indicating both the attitude and operating conditions of the aircraft. For this purpose, various measuring instruments and relative indicators are normally provided to supply the pilot with all the necessary flight control information. The indicators must obviously be installed on the aircraft instrument panel to give the pilot a clear view of the most important parameter values in terms of flight safety, while secondary indicators may be installed in peripheral areas.
In particular, it is essential that the pilot be provided with sufficient information to assess residual engine power and so safely determine whether or not flight conditions are compatible with engine efficiency, and which manoeuvres can or cannot be performed. In turbine engine aircraft, the operating conditions of each engine are basically defined by three engine parameters: output torque, turbine rotation speed, and turbine input (or reference) temperature. These parameters are related to power output, and have different operating limits depending on engine speed and ambient conditions (e.g. pressure and temperature, which vary considerably with altitude). In other words, varying power demand of the engine produces variations in all three engine parameters, but by amounts depending on engine speed and ambient conditions. As a result, the first parameter to exceed a respective operating limit need not necessarily always be the same, depending on flight conditions, and the relationship between the variations of two parameters is also affected by operating conditions.
Conventional instruments, however, indicate the power output of each engine basically in the form of a torque reading, which the pilot interprets more or less intuitively. Torque, however, does not give an absolute indication of the residual power margin available. In fact, depending on operating conditions, one of the other two engine parameters may exceed a respective operative limit though the instruments still indicate a residual torque margin. In other words, power margin and engine operating condition assessment depends on the pilot's experience and on combined monitoring of various indicators. In critical flight conditions, however, assessment in this way may take too long, thus constituting a safety hazard, and may even be erroneous. Moreover, the large number of parameters to be monitored results in crowding of the instrument panel, especially in the case of dual controls, which means all the indicators must also be duplicated. As a result, instrument readings are made difficult and, more importantly, slower, on account of the pilot's difficulty in immediately focusing solely on the main instruments (in themselves numerous). In difficult or even emergency flight conditions, such a situation may prove extremely hazardous.